Engineering of a β-galactosidase from Bacillus coagulans to relieve product inhibition and improve hydrolysis performance

Abstract

Most 0-galactosidases reported are sensitive to the end product (galactose), making it the rate-limiting component for the efficient degradation of lactose through the enzymatic route. Therefore, there is ongoing interest in searching for galactose-tolerant 0-galactosidases. In the present study, the predicted galactose-binding residues of 0-galactosidase from Bacillus coagulans, which were determined by molecular docking, were selected for alanine substitution. The asparagine residue at position 148 (N148) is correlated with the reduction of galactose inhibition. Saturation mutations revealed that the N148C, N148D, N148S, and N148G mutants exhibited weaker galactose inhibition effects. The N148D mutant was used for lactose hydrolysis and exhibited a higher hydrolytic rate. Molecular dynamics revealed that the root mean square deviation and gyration radius of the N148D-galactose complex were higher than those of wild-type enzyme-galactose complex. In addition, the N148D mutant had a higher absolute binding free -energy value. All these factors may lead to a lower affinity between galactose and the mutant enzyme. The use of mutant enzyme may have potential value in lactose hydrolysis.